1. Field of the Invention
The present invention relates to a cooling structure for a projector and a method of controlling such a cooling structure.
2. Description of the Related Art
Heretofore, projectors have been cooled by a fan which is operated under a fixed drive voltage of 12 V, for example. However, because of growing demands for low-noise environments, it is general practice to employ a variable-speed fan for cooling projectors, and lower the rotational speed of the variable-speed fan when the ambient temperature around the projector drops below an allowable temperature for various components of the projector. The variable-speed fan is associated with a sensor for detecting the ambient temperature, and the rotational speed of the variable-speed fan is changed depending on the detected ambient temperature.
According to another speed control scheme, rather than the variable-speed fan changing the rotational speed thereof, the projector itself changes the rotational speed of the variable-speed fan. Specifically, a temperature sensor is installed in the projector itself, and a drive voltage for the fan is established based on a temperature detected by the temperature sensor to control the rotational speed of the fan.
Both the above conventional arrangements change the rotational speed of the fan for thereby cooling the components of the projector and reducing noise produced by the fan.
However, there is a certain limitation on the voltages that can be applied to fans. For example, a general DC fan is used in a voltage range from 7 V to 13 V, and the range of rotational speeds at which the fan can rotate depends on that voltage range. Therefore, an upper limit for ambient temperatures for the installation of a projector should be selected such that the temperatures of the components of the projector will not exceed an allowable level when the fan rotates at a maximum rotational speed. If the upper limit for ambient temperatures for the installation of a projector is to be increased, then the projector should incorporate a fan of higher cooling capability, i.e., a fan having a larger diameter or a fan capable of rotating at a higher rotational speed. However, such a fan of higher cooling capability presents a major obstacle to efforts to reduce the size and noise of the projector.